Scarlet fever is a disease caused by an infection with group A beta-hemolytic streptococcal bacteria that occurs in a small percentage of people with strep throat. The illness typically begins with a fever and sore throat. It may be accompanied by chills, vomiting, abdominal pain and malaise. The streptococcal bacteria produces a toxin that causes a rash that appears one to two days after the onset of illness. The rash initially appears on the neck and chest, then spreads over the body. While the rash is still red, the patient may develop Pastia's lines, bright red coloration of the creases under the arm and in the groin.